Standards Compliance

Ibex is a standards-compliant 32 bit RISC-V processor. It follows these specifications:

Many features in the RISC-V specification are optional, and Ibex can be parametrized to enable or disable some of them.

Ibex can be parametrized to support either of the following two instruction sets.

  • The RV32I Base Integer Instruction Set, version 2.1

  • The RV32E Base Integer Instruction Set, version 1.9 (draft from June 8, 2019)

In addition, the following instruction set extensions are available.

Table 1 Ibex Instruction Set Extensions




C: Standard Extension for Compressed Instructions


always enabled

M: Standard Extension for Integer Multiplication and Division



B: Standard Extension for Bit-Manipulation Instructions

1.0.0 + 0.93 1


Zicsr: Control and Status Register Instructions


always enabled

Zifencei: Instruction-Fetch Fence


always enabled

Smepmp - PMP Enhancements for memory access and execution prevention on Machine mode


always enabled in configurations with PMP see PMP Enhancements

Ibex currently supports the following features according to the RISC-V Privileged Specification, version 1.12.



Ibex fully implements the ratified version 1.0.0 of the RISC-V Bit-Manipulation Extension including the Zba, Zbb, Zbc and Zbs sub-extensions. In addition, Ibex also supports the remaining Zbe, Zbf, Zbp, Zbr and Zbt sub-extensions as defined in draft version 0.93 of the RISC-V Bit-Manipulation Extension. Note that the latter sub-extensions may change before being ratified as a standard by the RISC-V Foundation. Ibex will be updated to match future versions of the specification. Prior to ratification this may involve backwards incompatible changes. Additionally, neither GCC or Clang have committed to maintaining support upstream for unratified versions of the specification.